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-rw-r--r--mm/ksm.c3230
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diff --git a/mm/ksm.c b/mm/ksm.c
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+++ b/mm/ksm.c
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+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Memory merging support.
+ *
+ * This code enables dynamic sharing of identical pages found in different
+ * memory areas, even if they are not shared by fork()
+ *
+ * Copyright (C) 2008-2009 Red Hat, Inc.
+ * Authors:
+ * Izik Eidus
+ * Andrea Arcangeli
+ * Chris Wright
+ * Hugh Dickins
+ */
+
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/mm_inline.h>
+#include <linux/fs.h>
+#include <linux/mman.h>
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/coredump.h>
+#include <linux/rwsem.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/spinlock.h>
+#include <linux/xxhash.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/wait.h>
+#include <linux/slab.h>
+#include <linux/rbtree.h>
+#include <linux/memory.h>
+#include <linux/mmu_notifier.h>
+#include <linux/swap.h>
+#include <linux/ksm.h>
+#include <linux/hashtable.h>
+#include <linux/freezer.h>
+#include <linux/oom.h>
+#include <linux/numa.h>
+
+#include <asm/tlbflush.h>
+#include "internal.h"
+#include "mm_slot.h"
+
+#ifdef CONFIG_NUMA
+#define NUMA(x) (x)
+#define DO_NUMA(x) do { (x); } while (0)
+#else
+#define NUMA(x) (0)
+#define DO_NUMA(x) do { } while (0)
+#endif
+
+/**
+ * DOC: Overview
+ *
+ * A few notes about the KSM scanning process,
+ * to make it easier to understand the data structures below:
+ *
+ * In order to reduce excessive scanning, KSM sorts the memory pages by their
+ * contents into a data structure that holds pointers to the pages' locations.
+ *
+ * Since the contents of the pages may change at any moment, KSM cannot just
+ * insert the pages into a normal sorted tree and expect it to find anything.
+ * Therefore KSM uses two data structures - the stable and the unstable tree.
+ *
+ * The stable tree holds pointers to all the merged pages (ksm pages), sorted
+ * by their contents. Because each such page is write-protected, searching on
+ * this tree is fully assured to be working (except when pages are unmapped),
+ * and therefore this tree is called the stable tree.
+ *
+ * The stable tree node includes information required for reverse
+ * mapping from a KSM page to virtual addresses that map this page.
+ *
+ * In order to avoid large latencies of the rmap walks on KSM pages,
+ * KSM maintains two types of nodes in the stable tree:
+ *
+ * * the regular nodes that keep the reverse mapping structures in a
+ * linked list
+ * * the "chains" that link nodes ("dups") that represent the same
+ * write protected memory content, but each "dup" corresponds to a
+ * different KSM page copy of that content
+ *
+ * Internally, the regular nodes, "dups" and "chains" are represented
+ * using the same struct ksm_stable_node structure.
+ *
+ * In addition to the stable tree, KSM uses a second data structure called the
+ * unstable tree: this tree holds pointers to pages which have been found to
+ * be "unchanged for a period of time". The unstable tree sorts these pages
+ * by their contents, but since they are not write-protected, KSM cannot rely
+ * upon the unstable tree to work correctly - the unstable tree is liable to
+ * be corrupted as its contents are modified, and so it is called unstable.
+ *
+ * KSM solves this problem by several techniques:
+ *
+ * 1) The unstable tree is flushed every time KSM completes scanning all
+ * memory areas, and then the tree is rebuilt again from the beginning.
+ * 2) KSM will only insert into the unstable tree, pages whose hash value
+ * has not changed since the previous scan of all memory areas.
+ * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
+ * colors of the nodes and not on their contents, assuring that even when
+ * the tree gets "corrupted" it won't get out of balance, so scanning time
+ * remains the same (also, searching and inserting nodes in an rbtree uses
+ * the same algorithm, so we have no overhead when we flush and rebuild).
+ * 4) KSM never flushes the stable tree, which means that even if it were to
+ * take 10 attempts to find a page in the unstable tree, once it is found,
+ * it is secured in the stable tree. (When we scan a new page, we first
+ * compare it against the stable tree, and then against the unstable tree.)
+ *
+ * If the merge_across_nodes tunable is unset, then KSM maintains multiple
+ * stable trees and multiple unstable trees: one of each for each NUMA node.
+ */
+
+/**
+ * struct ksm_mm_slot - ksm information per mm that is being scanned
+ * @slot: hash lookup from mm to mm_slot
+ * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
+ */
+struct ksm_mm_slot {
+ struct mm_slot slot;
+ struct ksm_rmap_item *rmap_list;
+};
+
+/**
+ * struct ksm_scan - cursor for scanning
+ * @mm_slot: the current mm_slot we are scanning
+ * @address: the next address inside that to be scanned
+ * @rmap_list: link to the next rmap to be scanned in the rmap_list
+ * @seqnr: count of completed full scans (needed when removing unstable node)
+ *
+ * There is only the one ksm_scan instance of this cursor structure.
+ */
+struct ksm_scan {
+ struct ksm_mm_slot *mm_slot;
+ unsigned long address;
+ struct ksm_rmap_item **rmap_list;
+ unsigned long seqnr;
+};
+
+/**
+ * struct ksm_stable_node - node of the stable rbtree
+ * @node: rb node of this ksm page in the stable tree
+ * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
+ * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
+ * @list: linked into migrate_nodes, pending placement in the proper node tree
+ * @hlist: hlist head of rmap_items using this ksm page
+ * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
+ * @chain_prune_time: time of the last full garbage collection
+ * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
+ * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
+ */
+struct ksm_stable_node {
+ union {
+ struct rb_node node; /* when node of stable tree */
+ struct { /* when listed for migration */
+ struct list_head *head;
+ struct {
+ struct hlist_node hlist_dup;
+ struct list_head list;
+ };
+ };
+ };
+ struct hlist_head hlist;
+ union {
+ unsigned long kpfn;
+ unsigned long chain_prune_time;
+ };
+ /*
+ * STABLE_NODE_CHAIN can be any negative number in
+ * rmap_hlist_len negative range, but better not -1 to be able
+ * to reliably detect underflows.
+ */
+#define STABLE_NODE_CHAIN -1024
+ int rmap_hlist_len;
+#ifdef CONFIG_NUMA
+ int nid;
+#endif
+};
+
+/**
+ * struct ksm_rmap_item - reverse mapping item for virtual addresses
+ * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
+ * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
+ * @nid: NUMA node id of unstable tree in which linked (may not match page)
+ * @mm: the memory structure this rmap_item is pointing into
+ * @address: the virtual address this rmap_item tracks (+ flags in low bits)
+ * @oldchecksum: previous checksum of the page at that virtual address
+ * @node: rb node of this rmap_item in the unstable tree
+ * @head: pointer to stable_node heading this list in the stable tree
+ * @hlist: link into hlist of rmap_items hanging off that stable_node
+ */
+struct ksm_rmap_item {
+ struct ksm_rmap_item *rmap_list;
+ union {
+ struct anon_vma *anon_vma; /* when stable */
+#ifdef CONFIG_NUMA
+ int nid; /* when node of unstable tree */
+#endif
+ };
+ struct mm_struct *mm;
+ unsigned long address; /* + low bits used for flags below */
+ unsigned int oldchecksum; /* when unstable */
+ union {
+ struct rb_node node; /* when node of unstable tree */
+ struct { /* when listed from stable tree */
+ struct ksm_stable_node *head;
+ struct hlist_node hlist;
+ };
+ };
+};
+
+#define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
+#define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
+#define STABLE_FLAG 0x200 /* is listed from the stable tree */
+
+/* The stable and unstable tree heads */
+static struct rb_root one_stable_tree[1] = { RB_ROOT };
+static struct rb_root one_unstable_tree[1] = { RB_ROOT };
+static struct rb_root *root_stable_tree = one_stable_tree;
+static struct rb_root *root_unstable_tree = one_unstable_tree;
+
+/* Recently migrated nodes of stable tree, pending proper placement */
+static LIST_HEAD(migrate_nodes);
+#define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
+
+#define MM_SLOTS_HASH_BITS 10
+static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
+
+static struct ksm_mm_slot ksm_mm_head = {
+ .slot.mm_node = LIST_HEAD_INIT(ksm_mm_head.slot.mm_node),
+};
+static struct ksm_scan ksm_scan = {
+ .mm_slot = &ksm_mm_head,
+};
+
+static struct kmem_cache *rmap_item_cache;
+static struct kmem_cache *stable_node_cache;
+static struct kmem_cache *mm_slot_cache;
+
+/* The number of nodes in the stable tree */
+static unsigned long ksm_pages_shared;
+
+/* The number of page slots additionally sharing those nodes */
+static unsigned long ksm_pages_sharing;
+
+/* The number of nodes in the unstable tree */
+static unsigned long ksm_pages_unshared;
+
+/* The number of rmap_items in use: to calculate pages_volatile */
+static unsigned long ksm_rmap_items;
+
+/* The number of stable_node chains */
+static unsigned long ksm_stable_node_chains;
+
+/* The number of stable_node dups linked to the stable_node chains */
+static unsigned long ksm_stable_node_dups;
+
+/* Delay in pruning stale stable_node_dups in the stable_node_chains */
+static unsigned int ksm_stable_node_chains_prune_millisecs = 2000;
+
+/* Maximum number of page slots sharing a stable node */
+static int ksm_max_page_sharing = 256;
+
+/* Number of pages ksmd should scan in one batch */
+static unsigned int ksm_thread_pages_to_scan = 100;
+
+/* Milliseconds ksmd should sleep between batches */
+static unsigned int ksm_thread_sleep_millisecs = 20;
+
+/* Checksum of an empty (zeroed) page */
+static unsigned int zero_checksum __read_mostly;
+
+/* Whether to merge empty (zeroed) pages with actual zero pages */
+static bool ksm_use_zero_pages __read_mostly;
+
+#ifdef CONFIG_NUMA
+/* Zeroed when merging across nodes is not allowed */
+static unsigned int ksm_merge_across_nodes = 1;
+static int ksm_nr_node_ids = 1;
+#else
+#define ksm_merge_across_nodes 1U
+#define ksm_nr_node_ids 1
+#endif
+
+#define KSM_RUN_STOP 0
+#define KSM_RUN_MERGE 1
+#define KSM_RUN_UNMERGE 2
+#define KSM_RUN_OFFLINE 4
+static unsigned long ksm_run = KSM_RUN_STOP;
+static void wait_while_offlining(void);
+
+static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
+static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
+static DEFINE_MUTEX(ksm_thread_mutex);
+static DEFINE_SPINLOCK(ksm_mmlist_lock);
+
+#define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create(#__struct,\
+ sizeof(struct __struct), __alignof__(struct __struct),\
+ (__flags), NULL)
+
+static int __init ksm_slab_init(void)
+{
+ rmap_item_cache = KSM_KMEM_CACHE(ksm_rmap_item, 0);
+ if (!rmap_item_cache)
+ goto out;
+
+ stable_node_cache = KSM_KMEM_CACHE(ksm_stable_node, 0);
+ if (!stable_node_cache)
+ goto out_free1;
+
+ mm_slot_cache = KSM_KMEM_CACHE(ksm_mm_slot, 0);
+ if (!mm_slot_cache)
+ goto out_free2;
+
+ return 0;
+
+out_free2:
+ kmem_cache_destroy(stable_node_cache);
+out_free1:
+ kmem_cache_destroy(rmap_item_cache);
+out:
+ return -ENOMEM;
+}
+
+static void __init ksm_slab_free(void)
+{
+ kmem_cache_destroy(mm_slot_cache);
+ kmem_cache_destroy(stable_node_cache);
+ kmem_cache_destroy(rmap_item_cache);
+ mm_slot_cache = NULL;
+}
+
+static __always_inline bool is_stable_node_chain(struct ksm_stable_node *chain)
+{
+ return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
+}
+
+static __always_inline bool is_stable_node_dup(struct ksm_stable_node *dup)
+{
+ return dup->head == STABLE_NODE_DUP_HEAD;
+}
+
+static inline void stable_node_chain_add_dup(struct ksm_stable_node *dup,
+ struct ksm_stable_node *chain)
+{
+ VM_BUG_ON(is_stable_node_dup(dup));
+ dup->head = STABLE_NODE_DUP_HEAD;
+ VM_BUG_ON(!is_stable_node_chain(chain));
+ hlist_add_head(&dup->hlist_dup, &chain->hlist);
+ ksm_stable_node_dups++;
+}
+
+static inline void __stable_node_dup_del(struct ksm_stable_node *dup)
+{
+ VM_BUG_ON(!is_stable_node_dup(dup));
+ hlist_del(&dup->hlist_dup);
+ ksm_stable_node_dups--;
+}
+
+static inline void stable_node_dup_del(struct ksm_stable_node *dup)
+{
+ VM_BUG_ON(is_stable_node_chain(dup));
+ if (is_stable_node_dup(dup))
+ __stable_node_dup_del(dup);
+ else
+ rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
+#ifdef CONFIG_DEBUG_VM
+ dup->head = NULL;
+#endif
+}
+
+static inline struct ksm_rmap_item *alloc_rmap_item(void)
+{
+ struct ksm_rmap_item *rmap_item;
+
+ rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
+ __GFP_NORETRY | __GFP_NOWARN);
+ if (rmap_item)
+ ksm_rmap_items++;
+ return rmap_item;
+}
+
+static inline void free_rmap_item(struct ksm_rmap_item *rmap_item)
+{
+ ksm_rmap_items--;
+ rmap_item->mm->ksm_rmap_items--;
+ rmap_item->mm = NULL; /* debug safety */
+ kmem_cache_free(rmap_item_cache, rmap_item);
+}
+
+static inline struct ksm_stable_node *alloc_stable_node(void)
+{
+ /*
+ * The allocation can take too long with GFP_KERNEL when memory is under
+ * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
+ * grants access to memory reserves, helping to avoid this problem.
+ */
+ return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
+}
+
+static inline void free_stable_node(struct ksm_stable_node *stable_node)
+{
+ VM_BUG_ON(stable_node->rmap_hlist_len &&
+ !is_stable_node_chain(stable_node));
+ kmem_cache_free(stable_node_cache, stable_node);
+}
+
+/*
+ * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
+ * page tables after it has passed through ksm_exit() - which, if necessary,
+ * takes mmap_lock briefly to serialize against them. ksm_exit() does not set
+ * a special flag: they can just back out as soon as mm_users goes to zero.
+ * ksm_test_exit() is used throughout to make this test for exit: in some
+ * places for correctness, in some places just to avoid unnecessary work.
+ */
+static inline bool ksm_test_exit(struct mm_struct *mm)
+{
+ return atomic_read(&mm->mm_users) == 0;
+}
+
+/*
+ * We use break_ksm to break COW on a ksm page: it's a stripped down
+ *
+ * if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
+ * put_page(page);
+ *
+ * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
+ * in case the application has unmapped and remapped mm,addr meanwhile.
+ * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
+ * mmap of /dev/mem, where we would not want to touch it.
+ *
+ * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
+ * of the process that owns 'vma'. We also do not want to enforce
+ * protection keys here anyway.
+ */
+static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
+{
+ struct page *page;
+ vm_fault_t ret = 0;
+
+ do {
+ cond_resched();
+ page = follow_page(vma, addr,
+ FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
+ if (IS_ERR_OR_NULL(page))
+ break;
+ if (PageKsm(page))
+ ret = handle_mm_fault(vma, addr,
+ FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
+ NULL);
+ else
+ ret = VM_FAULT_WRITE;
+ put_page(page);
+ } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
+ /*
+ * We must loop because handle_mm_fault() may back out if there's
+ * any difficulty e.g. if pte accessed bit gets updated concurrently.
+ *
+ * VM_FAULT_WRITE is what we have been hoping for: it indicates that
+ * COW has been broken, even if the vma does not permit VM_WRITE;
+ * but note that a concurrent fault might break PageKsm for us.
+ *
+ * VM_FAULT_SIGBUS could occur if we race with truncation of the
+ * backing file, which also invalidates anonymous pages: that's
+ * okay, that truncation will have unmapped the PageKsm for us.
+ *
+ * VM_FAULT_OOM: at the time of writing (late July 2009), setting
+ * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
+ * current task has TIF_MEMDIE set, and will be OOM killed on return
+ * to user; and ksmd, having no mm, would never be chosen for that.
+ *
+ * But if the mm is in a limited mem_cgroup, then the fault may fail
+ * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
+ * even ksmd can fail in this way - though it's usually breaking ksm
+ * just to undo a merge it made a moment before, so unlikely to oom.
+ *
+ * That's a pity: we might therefore have more kernel pages allocated
+ * than we're counting as nodes in the stable tree; but ksm_do_scan
+ * will retry to break_cow on each pass, so should recover the page
+ * in due course. The important thing is to not let VM_MERGEABLE
+ * be cleared while any such pages might remain in the area.
+ */
+ return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
+}
+
+static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
+ unsigned long addr)
+{
+ struct vm_area_struct *vma;
+ if (ksm_test_exit(mm))
+ return NULL;
+ vma = vma_lookup(mm, addr);
+ if (!vma || !(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
+ return NULL;
+ return vma;
+}
+
+static void break_cow(struct ksm_rmap_item *rmap_item)
+{
+ struct mm_struct *mm = rmap_item->mm;
+ unsigned long addr = rmap_item->address;
+ struct vm_area_struct *vma;
+
+ /*
+ * It is not an accident that whenever we want to break COW
+ * to undo, we also need to drop a reference to the anon_vma.
+ */
+ put_anon_vma(rmap_item->anon_vma);
+
+ mmap_read_lock(mm);
+ vma = find_mergeable_vma(mm, addr);
+ if (vma)
+ break_ksm(vma, addr);
+ mmap_read_unlock(mm);
+}
+
+static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item)
+{
+ struct mm_struct *mm = rmap_item->mm;
+ unsigned long addr = rmap_item->address;
+ struct vm_area_struct *vma;
+ struct page *page;
+
+ mmap_read_lock(mm);
+ vma = find_mergeable_vma(mm, addr);
+ if (!vma)
+ goto out;
+
+ page = follow_page(vma, addr, FOLL_GET);
+ if (IS_ERR_OR_NULL(page))
+ goto out;
+ if (is_zone_device_page(page))
+ goto out_putpage;
+ if (PageAnon(page)) {
+ flush_anon_page(vma, page, addr);
+ flush_dcache_page(page);
+ } else {
+out_putpage:
+ put_page(page);
+out:
+ page = NULL;
+ }
+ mmap_read_unlock(mm);
+ return page;
+}
+
+/*
+ * This helper is used for getting right index into array of tree roots.
+ * When merge_across_nodes knob is set to 1, there are only two rb-trees for
+ * stable and unstable pages from all nodes with roots in index 0. Otherwise,
+ * every node has its own stable and unstable tree.
+ */
+static inline int get_kpfn_nid(unsigned long kpfn)
+{
+ return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
+}
+
+static struct ksm_stable_node *alloc_stable_node_chain(struct ksm_stable_node *dup,
+ struct rb_root *root)
+{
+ struct ksm_stable_node *chain = alloc_stable_node();
+ VM_BUG_ON(is_stable_node_chain(dup));
+ if (likely(chain)) {
+ INIT_HLIST_HEAD(&chain->hlist);
+ chain->chain_prune_time = jiffies;
+ chain->rmap_hlist_len = STABLE_NODE_CHAIN;
+#if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
+ chain->nid = NUMA_NO_NODE; /* debug */
+#endif
+ ksm_stable_node_chains++;
+
+ /*
+ * Put the stable node chain in the first dimension of
+ * the stable tree and at the same time remove the old
+ * stable node.
+ */
+ rb_replace_node(&dup->node, &chain->node, root);
+
+ /*
+ * Move the old stable node to the second dimension
+ * queued in the hlist_dup. The invariant is that all
+ * dup stable_nodes in the chain->hlist point to pages
+ * that are write protected and have the exact same
+ * content.
+ */
+ stable_node_chain_add_dup(dup, chain);
+ }
+ return chain;
+}
+
+static inline void free_stable_node_chain(struct ksm_stable_node *chain,
+ struct rb_root *root)
+{
+ rb_erase(&chain->node, root);
+ free_stable_node(chain);
+ ksm_stable_node_chains--;
+}
+
+static void remove_node_from_stable_tree(struct ksm_stable_node *stable_node)
+{
+ struct ksm_rmap_item *rmap_item;
+
+ /* check it's not STABLE_NODE_CHAIN or negative */
+ BUG_ON(stable_node->rmap_hlist_len < 0);
+
+ hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
+ if (rmap_item->hlist.next)
+ ksm_pages_sharing--;
+ else
+ ksm_pages_shared--;
+
+ rmap_item->mm->ksm_merging_pages--;
+
+ VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
+ stable_node->rmap_hlist_len--;
+ put_anon_vma(rmap_item->anon_vma);
+ rmap_item->address &= PAGE_MASK;
+ cond_resched();
+ }
+
+ /*
+ * We need the second aligned pointer of the migrate_nodes
+ * list_head to stay clear from the rb_parent_color union
+ * (aligned and different than any node) and also different
+ * from &migrate_nodes. This will verify that future list.h changes
+ * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
+ */
+ BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
+ BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
+
+ if (stable_node->head == &migrate_nodes)
+ list_del(&stable_node->list);
+ else
+ stable_node_dup_del(stable_node);
+ free_stable_node(stable_node);
+}
+
+enum get_ksm_page_flags {
+ GET_KSM_PAGE_NOLOCK,
+ GET_KSM_PAGE_LOCK,
+ GET_KSM_PAGE_TRYLOCK
+};
+
+/*
+ * get_ksm_page: checks if the page indicated by the stable node
+ * is still its ksm page, despite having held no reference to it.
+ * In which case we can trust the content of the page, and it
+ * returns the gotten page; but if the page has now been zapped,
+ * remove the stale node from the stable tree and return NULL.
+ * But beware, the stable node's page might be being migrated.
+ *
+ * You would expect the stable_node to hold a reference to the ksm page.
+ * But if it increments the page's count, swapping out has to wait for
+ * ksmd to come around again before it can free the page, which may take
+ * seconds or even minutes: much too unresponsive. So instead we use a
+ * "keyhole reference": access to the ksm page from the stable node peeps
+ * out through its keyhole to see if that page still holds the right key,
+ * pointing back to this stable node. This relies on freeing a PageAnon
+ * page to reset its page->mapping to NULL, and relies on no other use of
+ * a page to put something that might look like our key in page->mapping.
+ * is on its way to being freed; but it is an anomaly to bear in mind.
+ */
+static struct page *get_ksm_page(struct ksm_stable_node *stable_node,
+ enum get_ksm_page_flags flags)
+{
+ struct page *page;
+ void *expected_mapping;
+ unsigned long kpfn;
+
+ expected_mapping = (void *)((unsigned long)stable_node |
+ PAGE_MAPPING_KSM);
+again:
+ kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
+ page = pfn_to_page(kpfn);
+ if (READ_ONCE(page->mapping) != expected_mapping)
+ goto stale;
+
+ /*
+ * We cannot do anything with the page while its refcount is 0.
+ * Usually 0 means free, or tail of a higher-order page: in which
+ * case this node is no longer referenced, and should be freed;
+ * however, it might mean that the page is under page_ref_freeze().
+ * The __remove_mapping() case is easy, again the node is now stale;
+ * the same is in reuse_ksm_page() case; but if page is swapcache
+ * in folio_migrate_mapping(), it might still be our page,
+ * in which case it's essential to keep the node.
+ */
+ while (!get_page_unless_zero(page)) {
+ /*
+ * Another check for page->mapping != expected_mapping would
+ * work here too. We have chosen the !PageSwapCache test to
+ * optimize the common case, when the page is or is about to
+ * be freed: PageSwapCache is cleared (under spin_lock_irq)
+ * in the ref_freeze section of __remove_mapping(); but Anon
+ * page->mapping reset to NULL later, in free_pages_prepare().
+ */
+ if (!PageSwapCache(page))
+ goto stale;
+ cpu_relax();
+ }
+
+ if (READ_ONCE(page->mapping) != expected_mapping) {
+ put_page(page);
+ goto stale;
+ }
+
+ if (flags == GET_KSM_PAGE_TRYLOCK) {
+ if (!trylock_page(page)) {
+ put_page(page);
+ return ERR_PTR(-EBUSY);
+ }
+ } else if (flags == GET_KSM_PAGE_LOCK)
+ lock_page(page);
+
+ if (flags != GET_KSM_PAGE_NOLOCK) {
+ if (READ_ONCE(page->mapping) != expected_mapping) {
+ unlock_page(page);
+ put_page(page);
+ goto stale;
+ }
+ }
+ return page;
+
+stale:
+ /*
+ * We come here from above when page->mapping or !PageSwapCache
+ * suggests that the node is stale; but it might be under migration.
+ * We need smp_rmb(), matching the smp_wmb() in folio_migrate_ksm(),
+ * before checking whether node->kpfn has been changed.
+ */
+ smp_rmb();
+ if (READ_ONCE(stable_node->kpfn) != kpfn)
+ goto again;
+ remove_node_from_stable_tree(stable_node);
+ return NULL;
+}
+
+/*
+ * Removing rmap_item from stable or unstable tree.
+ * This function will clean the information from the stable/unstable tree.
+ */
+static void remove_rmap_item_from_tree(struct ksm_rmap_item *rmap_item)
+{
+ if (rmap_item->address & STABLE_FLAG) {
+ struct ksm_stable_node *stable_node;
+ struct page *page;
+
+ stable_node = rmap_item->head;
+ page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
+ if (!page)
+ goto out;
+
+ hlist_del(&rmap_item->hlist);
+ unlock_page(page);
+ put_page(page);
+
+ if (!hlist_empty(&stable_node->hlist))
+ ksm_pages_sharing--;
+ else
+ ksm_pages_shared--;
+
+ rmap_item->mm->ksm_merging_pages--;
+
+ VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
+ stable_node->rmap_hlist_len--;
+
+ put_anon_vma(rmap_item->anon_vma);
+ rmap_item->head = NULL;
+ rmap_item->address &= PAGE_MASK;
+
+ } else if (rmap_item->address & UNSTABLE_FLAG) {
+ unsigned char age;
+ /*
+ * Usually ksmd can and must skip the rb_erase, because
+ * root_unstable_tree was already reset to RB_ROOT.
+ * But be careful when an mm is exiting: do the rb_erase
+ * if this rmap_item was inserted by this scan, rather
+ * than left over from before.
+ */
+ age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
+ BUG_ON(age > 1);
+ if (!age)
+ rb_erase(&rmap_item->node,
+ root_unstable_tree + NUMA(rmap_item->nid));
+ ksm_pages_unshared--;
+ rmap_item->address &= PAGE_MASK;
+ }
+out:
+ cond_resched(); /* we're called from many long loops */
+}
+
+static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list)
+{
+ while (*rmap_list) {
+ struct ksm_rmap_item *rmap_item = *rmap_list;
+ *rmap_list = rmap_item->rmap_list;
+ remove_rmap_item_from_tree(rmap_item);
+ free_rmap_item(rmap_item);
+ }
+}
+
+/*
+ * Though it's very tempting to unmerge rmap_items from stable tree rather
+ * than check every pte of a given vma, the locking doesn't quite work for
+ * that - an rmap_item is assigned to the stable tree after inserting ksm
+ * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing
+ * rmap_items from parent to child at fork time (so as not to waste time
+ * if exit comes before the next scan reaches it).
+ *
+ * Similarly, although we'd like to remove rmap_items (so updating counts
+ * and freeing memory) when unmerging an area, it's easier to leave that
+ * to the next pass of ksmd - consider, for example, how ksmd might be
+ * in cmp_and_merge_page on one of the rmap_items we would be removing.
+ */
+static int unmerge_ksm_pages(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)
+{
+ unsigned long addr;
+ int err = 0;
+
+ for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
+ if (ksm_test_exit(vma->vm_mm))
+ break;
+ if (signal_pending(current))
+ err = -ERESTARTSYS;
+ else
+ err = break_ksm(vma, addr);
+ }
+ return err;
+}
+
+static inline struct ksm_stable_node *folio_stable_node(struct folio *folio)
+{
+ return folio_test_ksm(folio) ? folio_raw_mapping(folio) : NULL;
+}
+
+static inline struct ksm_stable_node *page_stable_node(struct page *page)
+{
+ return folio_stable_node(page_folio(page));
+}
+
+static inline void set_page_stable_node(struct page *page,
+ struct ksm_stable_node *stable_node)
+{
+ VM_BUG_ON_PAGE(PageAnon(page) && PageAnonExclusive(page), page);
+ page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
+}
+
+#ifdef CONFIG_SYSFS
+/*
+ * Only called through the sysfs control interface:
+ */
+static int remove_stable_node(struct ksm_stable_node *stable_node)
+{
+ struct page *page;
+ int err;
+
+ page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
+ if (!page) {
+ /*
+ * get_ksm_page did remove_node_from_stable_tree itself.
+ */
+ return 0;
+ }
+
+ /*
+ * Page could be still mapped if this races with __mmput() running in
+ * between ksm_exit() and exit_mmap(). Just refuse to let
+ * merge_across_nodes/max_page_sharing be switched.
+ */
+ err = -EBUSY;
+ if (!page_mapped(page)) {
+ /*
+ * The stable node did not yet appear stale to get_ksm_page(),
+ * since that allows for an unmapped ksm page to be recognized
+ * right up until it is freed; but the node is safe to remove.
+ * This page might be in a pagevec waiting to be freed,
+ * or it might be PageSwapCache (perhaps under writeback),
+ * or it might have been removed from swapcache a moment ago.
+ */
+ set_page_stable_node(page, NULL);
+ remove_node_from_stable_tree(stable_node);
+ err = 0;
+ }
+
+ unlock_page(page);
+ put_page(page);
+ return err;
+}
+
+static int remove_stable_node_chain(struct ksm_stable_node *stable_node,
+ struct rb_root *root)
+{
+ struct ksm_stable_node *dup;
+ struct hlist_node *hlist_safe;
+
+ if (!is_stable_node_chain(stable_node)) {
+ VM_BUG_ON(is_stable_node_dup(stable_node));
+ if (remove_stable_node(stable_node))
+ return true;
+ else
+ return false;
+ }
+
+ hlist_for_each_entry_safe(dup, hlist_safe,
+ &stable_node->hlist, hlist_dup) {
+ VM_BUG_ON(!is_stable_node_dup(dup));
+ if (remove_stable_node(dup))
+ return true;
+ }
+ BUG_ON(!hlist_empty(&stable_node->hlist));
+ free_stable_node_chain(stable_node, root);
+ return false;
+}
+
+static int remove_all_stable_nodes(void)
+{
+ struct ksm_stable_node *stable_node, *next;
+ int nid;
+ int err = 0;
+
+ for (nid = 0; nid < ksm_nr_node_ids; nid++) {
+ while (root_stable_tree[nid].rb_node) {
+ stable_node = rb_entry(root_stable_tree[nid].rb_node,
+ struct ksm_stable_node, node);
+ if (remove_stable_node_chain(stable_node,
+ root_stable_tree + nid)) {
+ err = -EBUSY;
+ break; /* proceed to next nid */
+ }
+ cond_resched();
+ }
+ }
+ list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
+ if (remove_stable_node(stable_node))
+ err = -EBUSY;
+ cond_resched();
+ }
+ return err;
+}
+
+static int unmerge_and_remove_all_rmap_items(void)
+{
+ struct ksm_mm_slot *mm_slot;
+ struct mm_slot *slot;
+ struct mm_struct *mm;
+ struct vm_area_struct *vma;
+ int err = 0;
+
+ spin_lock(&ksm_mmlist_lock);
+ slot = list_entry(ksm_mm_head.slot.mm_node.next,
+ struct mm_slot, mm_node);
+ ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+ spin_unlock(&ksm_mmlist_lock);
+
+ for (mm_slot = ksm_scan.mm_slot; mm_slot != &ksm_mm_head;
+ mm_slot = ksm_scan.mm_slot) {
+ VMA_ITERATOR(vmi, mm_slot->slot.mm, 0);
+
+ mm = mm_slot->slot.mm;
+ mmap_read_lock(mm);
+
+ /*
+ * Exit right away if mm is exiting to avoid lockdep issue in
+ * the maple tree
+ */
+ if (ksm_test_exit(mm))
+ goto mm_exiting;
+
+ for_each_vma(vmi, vma) {
+ if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
+ continue;
+ err = unmerge_ksm_pages(vma,
+ vma->vm_start, vma->vm_end);
+ if (err)
+ goto error;
+ }
+
+mm_exiting:
+ remove_trailing_rmap_items(&mm_slot->rmap_list);
+ mmap_read_unlock(mm);
+
+ spin_lock(&ksm_mmlist_lock);
+ slot = list_entry(mm_slot->slot.mm_node.next,
+ struct mm_slot, mm_node);
+ ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+ if (ksm_test_exit(mm)) {
+ hash_del(&mm_slot->slot.hash);
+ list_del(&mm_slot->slot.mm_node);
+ spin_unlock(&ksm_mmlist_lock);
+
+ mm_slot_free(mm_slot_cache, mm_slot);
+ clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+ mmdrop(mm);
+ } else
+ spin_unlock(&ksm_mmlist_lock);
+ }
+
+ /* Clean up stable nodes, but don't worry if some are still busy */
+ remove_all_stable_nodes();
+ ksm_scan.seqnr = 0;
+ return 0;
+
+error:
+ mmap_read_unlock(mm);
+ spin_lock(&ksm_mmlist_lock);
+ ksm_scan.mm_slot = &ksm_mm_head;
+ spin_unlock(&ksm_mmlist_lock);
+ return err;
+}
+#endif /* CONFIG_SYSFS */
+
+static u32 calc_checksum(struct page *page)
+{
+ u32 checksum;
+ void *addr = kmap_atomic(page);
+ checksum = xxhash(addr, PAGE_SIZE, 0);
+ kunmap_atomic(addr);
+ return checksum;
+}
+
+static int write_protect_page(struct vm_area_struct *vma, struct page *page,
+ pte_t *orig_pte)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ DEFINE_PAGE_VMA_WALK(pvmw, page, vma, 0, 0);
+ int swapped;
+ int err = -EFAULT;
+ struct mmu_notifier_range range;
+ bool anon_exclusive;
+
+ pvmw.address = page_address_in_vma(page, vma);
+ if (pvmw.address == -EFAULT)
+ goto out;
+
+ BUG_ON(PageTransCompound(page));
+
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
+ pvmw.address,
+ pvmw.address + PAGE_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+
+ if (!page_vma_mapped_walk(&pvmw))
+ goto out_mn;
+ if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
+ goto out_unlock;
+
+ anon_exclusive = PageAnonExclusive(page);
+ if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
+ (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
+ anon_exclusive || mm_tlb_flush_pending(mm)) {
+ pte_t entry;
+
+ swapped = PageSwapCache(page);
+ flush_cache_page(vma, pvmw.address, page_to_pfn(page));
+ /*
+ * Ok this is tricky, when get_user_pages_fast() run it doesn't
+ * take any lock, therefore the check that we are going to make
+ * with the pagecount against the mapcount is racy and
+ * O_DIRECT can happen right after the check.
+ * So we clear the pte and flush the tlb before the check
+ * this assure us that no O_DIRECT can happen after the check
+ * or in the middle of the check.
+ *
+ * No need to notify as we are downgrading page table to read
+ * only not changing it to point to a new page.
+ *
+ * See Documentation/mm/mmu_notifier.rst
+ */
+ entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
+ /*
+ * Check that no O_DIRECT or similar I/O is in progress on the
+ * page
+ */
+ if (page_mapcount(page) + 1 + swapped != page_count(page)) {
+ set_pte_at(mm, pvmw.address, pvmw.pte, entry);
+ goto out_unlock;
+ }
+
+ /* See page_try_share_anon_rmap(): clear PTE first. */
+ if (anon_exclusive && page_try_share_anon_rmap(page)) {
+ set_pte_at(mm, pvmw.address, pvmw.pte, entry);
+ goto out_unlock;
+ }
+
+ if (pte_dirty(entry))
+ set_page_dirty(page);
+
+ if (pte_protnone(entry))
+ entry = pte_mkclean(pte_clear_savedwrite(entry));
+ else
+ entry = pte_mkclean(pte_wrprotect(entry));
+ set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
+ }
+ *orig_pte = *pvmw.pte;
+ err = 0;
+
+out_unlock:
+ page_vma_mapped_walk_done(&pvmw);
+out_mn:
+ mmu_notifier_invalidate_range_end(&range);
+out:
+ return err;
+}
+
+/**
+ * replace_page - replace page in vma by new ksm page
+ * @vma: vma that holds the pte pointing to page
+ * @page: the page we are replacing by kpage
+ * @kpage: the ksm page we replace page by
+ * @orig_pte: the original value of the pte
+ *
+ * Returns 0 on success, -EFAULT on failure.
+ */
+static int replace_page(struct vm_area_struct *vma, struct page *page,
+ struct page *kpage, pte_t orig_pte)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ struct folio *folio;
+ pmd_t *pmd;
+ pmd_t pmde;
+ pte_t *ptep;
+ pte_t newpte;
+ spinlock_t *ptl;
+ unsigned long addr;
+ int err = -EFAULT;
+ struct mmu_notifier_range range;
+
+ addr = page_address_in_vma(page, vma);
+ if (addr == -EFAULT)
+ goto out;
+
+ pmd = mm_find_pmd(mm, addr);
+ if (!pmd)
+ goto out;
+ /*
+ * Some THP functions use the sequence pmdp_huge_clear_flush(), set_pmd_at()
+ * without holding anon_vma lock for write. So when looking for a
+ * genuine pmde (in which to find pte), test present and !THP together.
+ */
+ pmde = *pmd;
+ barrier();
+ if (!pmd_present(pmde) || pmd_trans_huge(pmde))
+ goto out;
+
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
+ addr + PAGE_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+
+ ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (!pte_same(*ptep, orig_pte)) {
+ pte_unmap_unlock(ptep, ptl);
+ goto out_mn;
+ }
+ VM_BUG_ON_PAGE(PageAnonExclusive(page), page);
+ VM_BUG_ON_PAGE(PageAnon(kpage) && PageAnonExclusive(kpage), kpage);
+
+ /*
+ * No need to check ksm_use_zero_pages here: we can only have a
+ * zero_page here if ksm_use_zero_pages was enabled already.
+ */
+ if (!is_zero_pfn(page_to_pfn(kpage))) {
+ get_page(kpage);
+ page_add_anon_rmap(kpage, vma, addr, RMAP_NONE);
+ newpte = mk_pte(kpage, vma->vm_page_prot);
+ } else {
+ newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
+ vma->vm_page_prot));
+ /*
+ * We're replacing an anonymous page with a zero page, which is
+ * not anonymous. We need to do proper accounting otherwise we
+ * will get wrong values in /proc, and a BUG message in dmesg
+ * when tearing down the mm.
+ */
+ dec_mm_counter(mm, MM_ANONPAGES);
+ }
+
+ flush_cache_page(vma, addr, pte_pfn(*ptep));
+ /*
+ * No need to notify as we are replacing a read only page with another
+ * read only page with the same content.
+ *
+ * See Documentation/mm/mmu_notifier.rst
+ */
+ ptep_clear_flush(vma, addr, ptep);
+ set_pte_at_notify(mm, addr, ptep, newpte);
+
+ folio = page_folio(page);
+ page_remove_rmap(page, vma, false);
+ if (!folio_mapped(folio))
+ folio_free_swap(folio);
+ folio_put(folio);
+
+ pte_unmap_unlock(ptep, ptl);
+ err = 0;
+out_mn:
+ mmu_notifier_invalidate_range_end(&range);
+out:
+ return err;
+}
+
+/*
+ * try_to_merge_one_page - take two pages and merge them into one
+ * @vma: the vma that holds the pte pointing to page
+ * @page: the PageAnon page that we want to replace with kpage
+ * @kpage: the PageKsm page that we want to map instead of page,
+ * or NULL the first time when we want to use page as kpage.
+ *
+ * This function returns 0 if the pages were merged, -EFAULT otherwise.
+ */
+static int try_to_merge_one_page(struct vm_area_struct *vma,
+ struct page *page, struct page *kpage)
+{
+ pte_t orig_pte = __pte(0);
+ int err = -EFAULT;
+
+ if (page == kpage) /* ksm page forked */
+ return 0;
+
+ if (!PageAnon(page))
+ goto out;
+
+ /*
+ * We need the page lock to read a stable PageSwapCache in
+ * write_protect_page(). We use trylock_page() instead of
+ * lock_page() because we don't want to wait here - we
+ * prefer to continue scanning and merging different pages,
+ * then come back to this page when it is unlocked.
+ */
+ if (!trylock_page(page))
+ goto out;
+
+ if (PageTransCompound(page)) {
+ if (split_huge_page(page))
+ goto out_unlock;
+ }
+
+ /*
+ * If this anonymous page is mapped only here, its pte may need
+ * to be write-protected. If it's mapped elsewhere, all of its
+ * ptes are necessarily already write-protected. But in either
+ * case, we need to lock and check page_count is not raised.
+ */
+ if (write_protect_page(vma, page, &orig_pte) == 0) {
+ if (!kpage) {
+ /*
+ * While we hold page lock, upgrade page from
+ * PageAnon+anon_vma to PageKsm+NULL stable_node:
+ * stable_tree_insert() will update stable_node.
+ */
+ set_page_stable_node(page, NULL);
+ mark_page_accessed(page);
+ /*
+ * Page reclaim just frees a clean page with no dirty
+ * ptes: make sure that the ksm page would be swapped.
+ */
+ if (!PageDirty(page))
+ SetPageDirty(page);
+ err = 0;
+ } else if (pages_identical(page, kpage))
+ err = replace_page(vma, page, kpage, orig_pte);
+ }
+
+out_unlock:
+ unlock_page(page);
+out:
+ return err;
+}
+
+/*
+ * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
+ * but no new kernel page is allocated: kpage must already be a ksm page.
+ *
+ * This function returns 0 if the pages were merged, -EFAULT otherwise.
+ */
+static int try_to_merge_with_ksm_page(struct ksm_rmap_item *rmap_item,
+ struct page *page, struct page *kpage)
+{
+ struct mm_struct *mm = rmap_item->mm;
+ struct vm_area_struct *vma;
+ int err = -EFAULT;
+
+ mmap_read_lock(mm);
+ vma = find_mergeable_vma(mm, rmap_item->address);
+ if (!vma)
+ goto out;
+
+ err = try_to_merge_one_page(vma, page, kpage);
+ if (err)
+ goto out;
+
+ /* Unstable nid is in union with stable anon_vma: remove first */
+ remove_rmap_item_from_tree(rmap_item);
+
+ /* Must get reference to anon_vma while still holding mmap_lock */
+ rmap_item->anon_vma = vma->anon_vma;
+ get_anon_vma(vma->anon_vma);
+out:
+ mmap_read_unlock(mm);
+ return err;
+}
+
+/*
+ * try_to_merge_two_pages - take two identical pages and prepare them
+ * to be merged into one page.
+ *
+ * This function returns the kpage if we successfully merged two identical
+ * pages into one ksm page, NULL otherwise.
+ *
+ * Note that this function upgrades page to ksm page: if one of the pages
+ * is already a ksm page, try_to_merge_with_ksm_page should be used.
+ */
+static struct page *try_to_merge_two_pages(struct ksm_rmap_item *rmap_item,
+ struct page *page,
+ struct ksm_rmap_item *tree_rmap_item,
+ struct page *tree_page)
+{
+ int err;
+
+ err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
+ if (!err) {
+ err = try_to_merge_with_ksm_page(tree_rmap_item,
+ tree_page, page);
+ /*
+ * If that fails, we have a ksm page with only one pte
+ * pointing to it: so break it.
+ */
+ if (err)
+ break_cow(rmap_item);
+ }
+ return err ? NULL : page;
+}
+
+static __always_inline
+bool __is_page_sharing_candidate(struct ksm_stable_node *stable_node, int offset)
+{
+ VM_BUG_ON(stable_node->rmap_hlist_len < 0);
+ /*
+ * Check that at least one mapping still exists, otherwise
+ * there's no much point to merge and share with this
+ * stable_node, as the underlying tree_page of the other
+ * sharer is going to be freed soon.
+ */
+ return stable_node->rmap_hlist_len &&
+ stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
+}
+
+static __always_inline
+bool is_page_sharing_candidate(struct ksm_stable_node *stable_node)
+{
+ return __is_page_sharing_candidate(stable_node, 0);
+}
+
+static struct page *stable_node_dup(struct ksm_stable_node **_stable_node_dup,
+ struct ksm_stable_node **_stable_node,
+ struct rb_root *root,
+ bool prune_stale_stable_nodes)
+{
+ struct ksm_stable_node *dup, *found = NULL, *stable_node = *_stable_node;
+ struct hlist_node *hlist_safe;
+ struct page *_tree_page, *tree_page = NULL;
+ int nr = 0;
+ int found_rmap_hlist_len;
+
+ if (!prune_stale_stable_nodes ||
+ time_before(jiffies, stable_node->chain_prune_time +
+ msecs_to_jiffies(
+ ksm_stable_node_chains_prune_millisecs)))
+ prune_stale_stable_nodes = false;
+ else
+ stable_node->chain_prune_time = jiffies;
+
+ hlist_for_each_entry_safe(dup, hlist_safe,
+ &stable_node->hlist, hlist_dup) {
+ cond_resched();
+ /*
+ * We must walk all stable_node_dup to prune the stale
+ * stable nodes during lookup.
+ *
+ * get_ksm_page can drop the nodes from the
+ * stable_node->hlist if they point to freed pages
+ * (that's why we do a _safe walk). The "dup"
+ * stable_node parameter itself will be freed from
+ * under us if it returns NULL.
+ */
+ _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
+ if (!_tree_page)
+ continue;
+ nr += 1;
+ if (is_page_sharing_candidate(dup)) {
+ if (!found ||
+ dup->rmap_hlist_len > found_rmap_hlist_len) {
+ if (found)
+ put_page(tree_page);
+ found = dup;
+ found_rmap_hlist_len = found->rmap_hlist_len;
+ tree_page = _tree_page;
+
+ /* skip put_page for found dup */
+ if (!prune_stale_stable_nodes)
+ break;
+ continue;
+ }
+ }
+ put_page(_tree_page);
+ }
+
+ if (found) {
+ /*
+ * nr is counting all dups in the chain only if
+ * prune_stale_stable_nodes is true, otherwise we may
+ * break the loop at nr == 1 even if there are
+ * multiple entries.
+ */
+ if (prune_stale_stable_nodes && nr == 1) {
+ /*
+ * If there's not just one entry it would
+ * corrupt memory, better BUG_ON. In KSM
+ * context with no lock held it's not even
+ * fatal.
+ */
+ BUG_ON(stable_node->hlist.first->next);
+
+ /*
+ * There's just one entry and it is below the
+ * deduplication limit so drop the chain.
+ */
+ rb_replace_node(&stable_node->node, &found->node,
+ root);
+ free_stable_node(stable_node);
+ ksm_stable_node_chains--;
+ ksm_stable_node_dups--;
+ /*
+ * NOTE: the caller depends on the stable_node
+ * to be equal to stable_node_dup if the chain
+ * was collapsed.
+ */
+ *_stable_node = found;
+ /*
+ * Just for robustness, as stable_node is
+ * otherwise left as a stable pointer, the
+ * compiler shall optimize it away at build
+ * time.
+ */
+ stable_node = NULL;
+ } else if (stable_node->hlist.first != &found->hlist_dup &&
+ __is_page_sharing_candidate(found, 1)) {
+ /*
+ * If the found stable_node dup can accept one
+ * more future merge (in addition to the one
+ * that is underway) and is not at the head of
+ * the chain, put it there so next search will
+ * be quicker in the !prune_stale_stable_nodes
+ * case.
+ *
+ * NOTE: it would be inaccurate to use nr > 1
+ * instead of checking the hlist.first pointer
+ * directly, because in the
+ * prune_stale_stable_nodes case "nr" isn't
+ * the position of the found dup in the chain,
+ * but the total number of dups in the chain.
+ */
+ hlist_del(&found->hlist_dup);
+ hlist_add_head(&found->hlist_dup,
+ &stable_node->hlist);
+ }
+ }
+
+ *_stable_node_dup = found;
+ return tree_page;
+}
+
+static struct ksm_stable_node *stable_node_dup_any(struct ksm_stable_node *stable_node,
+ struct rb_root *root)
+{
+ if (!is_stable_node_chain(stable_node))
+ return stable_node;
+ if (hlist_empty(&stable_node->hlist)) {
+ free_stable_node_chain(stable_node, root);
+ return NULL;
+ }
+ return hlist_entry(stable_node->hlist.first,
+ typeof(*stable_node), hlist_dup);
+}
+
+/*
+ * Like for get_ksm_page, this function can free the *_stable_node and
+ * *_stable_node_dup if the returned tree_page is NULL.
+ *
+ * It can also free and overwrite *_stable_node with the found
+ * stable_node_dup if the chain is collapsed (in which case
+ * *_stable_node will be equal to *_stable_node_dup like if the chain
+ * never existed). It's up to the caller to verify tree_page is not
+ * NULL before dereferencing *_stable_node or *_stable_node_dup.
+ *
+ * *_stable_node_dup is really a second output parameter of this
+ * function and will be overwritten in all cases, the caller doesn't
+ * need to initialize it.
+ */
+static struct page *__stable_node_chain(struct ksm_stable_node **_stable_node_dup,
+ struct ksm_stable_node **_stable_node,
+ struct rb_root *root,
+ bool prune_stale_stable_nodes)
+{
+ struct ksm_stable_node *stable_node = *_stable_node;
+ if (!is_stable_node_chain(stable_node)) {
+ if (is_page_sharing_candidate(stable_node)) {
+ *_stable_node_dup = stable_node;
+ return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
+ }
+ /*
+ * _stable_node_dup set to NULL means the stable_node
+ * reached the ksm_max_page_sharing limit.
+ */
+ *_stable_node_dup = NULL;
+ return NULL;
+ }
+ return stable_node_dup(_stable_node_dup, _stable_node, root,
+ prune_stale_stable_nodes);
+}
+
+static __always_inline struct page *chain_prune(struct ksm_stable_node **s_n_d,
+ struct ksm_stable_node **s_n,
+ struct rb_root *root)
+{
+ return __stable_node_chain(s_n_d, s_n, root, true);
+}
+
+static __always_inline struct page *chain(struct ksm_stable_node **s_n_d,
+ struct ksm_stable_node *s_n,
+ struct rb_root *root)
+{
+ struct ksm_stable_node *old_stable_node = s_n;
+ struct page *tree_page;
+
+ tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
+ /* not pruning dups so s_n cannot have changed */
+ VM_BUG_ON(s_n != old_stable_node);
+ return tree_page;
+}
+
+/*
+ * stable_tree_search - search for page inside the stable tree
+ *
+ * This function checks if there is a page inside the stable tree
+ * with identical content to the page that we are scanning right now.
+ *
+ * This function returns the stable tree node of identical content if found,
+ * NULL otherwise.
+ */
+static struct page *stable_tree_search(struct page *page)
+{
+ int nid;
+ struct rb_root *root;
+ struct rb_node **new;
+ struct rb_node *parent;
+ struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
+ struct ksm_stable_node *page_node;
+
+ page_node = page_stable_node(page);
+ if (page_node && page_node->head != &migrate_nodes) {
+ /* ksm page forked */
+ get_page(page);
+ return page;
+ }
+
+ nid = get_kpfn_nid(page_to_pfn(page));
+ root = root_stable_tree + nid;
+again:
+ new = &root->rb_node;
+ parent = NULL;
+
+ while (*new) {
+ struct page *tree_page;
+ int ret;
+
+ cond_resched();
+ stable_node = rb_entry(*new, struct ksm_stable_node, node);
+ stable_node_any = NULL;
+ tree_page = chain_prune(&stable_node_dup, &stable_node, root);
+ /*
+ * NOTE: stable_node may have been freed by
+ * chain_prune() if the returned stable_node_dup is
+ * not NULL. stable_node_dup may have been inserted in
+ * the rbtree instead as a regular stable_node (in
+ * order to collapse the stable_node chain if a single
+ * stable_node dup was found in it). In such case the
+ * stable_node is overwritten by the callee to point
+ * to the stable_node_dup that was collapsed in the
+ * stable rbtree and stable_node will be equal to
+ * stable_node_dup like if the chain never existed.
+ */
+ if (!stable_node_dup) {
+ /*
+ * Either all stable_node dups were full in
+ * this stable_node chain, or this chain was
+ * empty and should be rb_erased.
+ */
+ stable_node_any = stable_node_dup_any(stable_node,
+ root);
+ if (!stable_node_any) {
+ /* rb_erase just run */
+ goto again;
+ }
+ /*
+ * Take any of the stable_node dups page of
+ * this stable_node chain to let the tree walk
+ * continue. All KSM pages belonging to the
+ * stable_node dups in a stable_node chain
+ * have the same content and they're
+ * write protected at all times. Any will work
+ * fine to continue the walk.
+ */
+ tree_page = get_ksm_page(stable_node_any,
+ GET_KSM_PAGE_NOLOCK);
+ }
+ VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
+ if (!tree_page) {
+ /*
+ * If we walked over a stale stable_node,
+ * get_ksm_page() will call rb_erase() and it
+ * may rebalance the tree from under us. So
+ * restart the search from scratch. Returning
+ * NULL would be safe too, but we'd generate
+ * false negative insertions just because some
+ * stable_node was stale.
+ */
+ goto again;
+ }
+
+ ret = memcmp_pages(page, tree_page);
+ put_page(tree_page);
+
+ parent = *new;
+ if (ret < 0)
+ new = &parent->rb_left;
+ else if (ret > 0)
+ new = &parent->rb_right;
+ else {
+ if (page_node) {
+ VM_BUG_ON(page_node->head != &migrate_nodes);
+ /*
+ * Test if the migrated page should be merged
+ * into a stable node dup. If the mapcount is
+ * 1 we can migrate it with another KSM page
+ * without adding it to the chain.
+ */
+ if (page_mapcount(page) > 1)
+ goto chain_append;
+ }
+
+ if (!stable_node_dup) {
+ /*
+ * If the stable_node is a chain and
+ * we got a payload match in memcmp
+ * but we cannot merge the scanned
+ * page in any of the existing
+ * stable_node dups because they're
+ * all full, we need to wait the
+ * scanned page to find itself a match
+ * in the unstable tree to create a
+ * brand new KSM page to add later to
+ * the dups of this stable_node.
+ */
+ return NULL;
+ }
+
+ /*
+ * Lock and unlock the stable_node's page (which
+ * might already have been migrated) so that page
+ * migration is sure to notice its raised count.
+ * It would be more elegant to return stable_node
+ * than kpage, but that involves more changes.
+ */
+ tree_page = get_ksm_page(stable_node_dup,
+ GET_KSM_PAGE_TRYLOCK);
+
+ if (PTR_ERR(tree_page) == -EBUSY)
+ return ERR_PTR(-EBUSY);
+
+ if (unlikely(!tree_page))
+ /*
+ * The tree may have been rebalanced,
+ * so re-evaluate parent and new.
+ */
+ goto again;
+ unlock_page(tree_page);
+
+ if (get_kpfn_nid(stable_node_dup->kpfn) !=
+ NUMA(stable_node_dup->nid)) {
+ put_page(tree_page);
+ goto replace;
+ }
+ return tree_page;
+ }
+ }
+
+ if (!page_node)
+ return NULL;
+
+ list_del(&page_node->list);
+ DO_NUMA(page_node->nid = nid);
+ rb_link_node(&page_node->node, parent, new);
+ rb_insert_color(&page_node->node, root);
+out:
+ if (is_page_sharing_candidate(page_node)) {
+ get_page(page);
+ return page;
+ } else
+ return NULL;
+
+replace:
+ /*
+ * If stable_node was a chain and chain_prune collapsed it,
+ * stable_node has been updated to be the new regular
+ * stable_node. A collapse of the chain is indistinguishable
+ * from the case there was no chain in the stable
+ * rbtree. Otherwise stable_node is the chain and
+ * stable_node_dup is the dup to replace.
+ */
+ if (stable_node_dup == stable_node) {
+ VM_BUG_ON(is_stable_node_chain(stable_node_dup));
+ VM_BUG_ON(is_stable_node_dup(stable_node_dup));
+ /* there is no chain */
+ if (page_node) {
+ VM_BUG_ON(page_node->head != &migrate_nodes);
+ list_del(&page_node->list);
+ DO_NUMA(page_node->nid = nid);
+ rb_replace_node(&stable_node_dup->node,
+ &page_node->node,
+ root);
+ if (is_page_sharing_candidate(page_node))
+ get_page(page);
+ else
+ page = NULL;
+ } else {
+ rb_erase(&stable_node_dup->node, root);
+ page = NULL;
+ }
+ } else {
+ VM_BUG_ON(!is_stable_node_chain(stable_node));
+ __stable_node_dup_del(stable_node_dup);
+ if (page_node) {
+ VM_BUG_ON(page_node->head != &migrate_nodes);
+ list_del(&page_node->list);
+ DO_NUMA(page_node->nid = nid);
+ stable_node_chain_add_dup(page_node, stable_node);
+ if (is_page_sharing_candidate(page_node))
+ get_page(page);
+ else
+ page = NULL;
+ } else {
+ page = NULL;
+ }
+ }
+ stable_node_dup->head = &migrate_nodes;
+ list_add(&stable_node_dup->list, stable_node_dup->head);
+ return page;
+
+chain_append:
+ /* stable_node_dup could be null if it reached the limit */
+ if (!stable_node_dup)
+ stable_node_dup = stable_node_any;
+ /*
+ * If stable_node was a chain and chain_prune collapsed it,
+ * stable_node has been updated to be the new regular
+ * stable_node. A collapse of the chain is indistinguishable
+ * from the case there was no chain in the stable
+ * rbtree. Otherwise stable_node is the chain and
+ * stable_node_dup is the dup to replace.
+ */
+ if (stable_node_dup == stable_node) {
+ VM_BUG_ON(is_stable_node_dup(stable_node_dup));
+ /* chain is missing so create it */
+ stable_node = alloc_stable_node_chain(stable_node_dup,
+ root);
+ if (!stable_node)
+ return NULL;
+ }
+ /*
+ * Add this stable_node dup that was
+ * migrated to the stable_node chain
+ * of the current nid for this page
+ * content.
+ */
+ VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
+ VM_BUG_ON(page_node->head != &migrate_nodes);
+ list_del(&page_node->list);
+ DO_NUMA(page_node->nid = nid);
+ stable_node_chain_add_dup(page_node, stable_node);
+ goto out;
+}
+
+/*
+ * stable_tree_insert - insert stable tree node pointing to new ksm page
+ * into the stable tree.
+ *
+ * This function returns the stable tree node just allocated on success,
+ * NULL otherwise.
+ */
+static struct ksm_stable_node *stable_tree_insert(struct page *kpage)
+{
+ int nid;
+ unsigned long kpfn;
+ struct rb_root *root;
+ struct rb_node **new;
+ struct rb_node *parent;
+ struct ksm_stable_node *stable_node, *stable_node_dup, *stable_node_any;
+ bool need_chain = false;
+
+ kpfn = page_to_pfn(kpage);
+ nid = get_kpfn_nid(kpfn);
+ root = root_stable_tree + nid;
+again:
+ parent = NULL;
+ new = &root->rb_node;
+
+ while (*new) {
+ struct page *tree_page;
+ int ret;
+
+ cond_resched();
+ stable_node = rb_entry(*new, struct ksm_stable_node, node);
+ stable_node_any = NULL;
+ tree_page = chain(&stable_node_dup, stable_node, root);
+ if (!stable_node_dup) {
+ /*
+ * Either all stable_node dups were full in
+ * this stable_node chain, or this chain was
+ * empty and should be rb_erased.
+ */
+ stable_node_any = stable_node_dup_any(stable_node,
+ root);
+ if (!stable_node_any) {
+ /* rb_erase just run */
+ goto again;
+ }
+ /*
+ * Take any of the stable_node dups page of
+ * this stable_node chain to let the tree walk
+ * continue. All KSM pages belonging to the
+ * stable_node dups in a stable_node chain
+ * have the same content and they're
+ * write protected at all times. Any will work
+ * fine to continue the walk.
+ */
+ tree_page = get_ksm_page(stable_node_any,
+ GET_KSM_PAGE_NOLOCK);
+ }
+ VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
+ if (!tree_page) {
+ /*
+ * If we walked over a stale stable_node,
+ * get_ksm_page() will call rb_erase() and it
+ * may rebalance the tree from under us. So
+ * restart the search from scratch. Returning
+ * NULL would be safe too, but we'd generate
+ * false negative insertions just because some
+ * stable_node was stale.
+ */
+ goto again;
+ }
+
+ ret = memcmp_pages(kpage, tree_page);
+ put_page(tree_page);
+
+ parent = *new;
+ if (ret < 0)
+ new = &parent->rb_left;
+ else if (ret > 0)
+ new = &parent->rb_right;
+ else {
+ need_chain = true;
+ break;
+ }
+ }
+
+ stable_node_dup = alloc_stable_node();
+ if (!stable_node_dup)
+ return NULL;
+
+ INIT_HLIST_HEAD(&stable_node_dup->hlist);
+ stable_node_dup->kpfn = kpfn;
+ set_page_stable_node(kpage, stable_node_dup);
+ stable_node_dup->rmap_hlist_len = 0;
+ DO_NUMA(stable_node_dup->nid = nid);
+ if (!need_chain) {
+ rb_link_node(&stable_node_dup->node, parent, new);
+ rb_insert_color(&stable_node_dup->node, root);
+ } else {
+ if (!is_stable_node_chain(stable_node)) {
+ struct ksm_stable_node *orig = stable_node;
+ /* chain is missing so create it */
+ stable_node = alloc_stable_node_chain(orig, root);
+ if (!stable_node) {
+ free_stable_node(stable_node_dup);
+ return NULL;
+ }
+ }
+ stable_node_chain_add_dup(stable_node_dup, stable_node);
+ }
+
+ return stable_node_dup;
+}
+
+/*
+ * unstable_tree_search_insert - search for identical page,
+ * else insert rmap_item into the unstable tree.
+ *
+ * This function searches for a page in the unstable tree identical to the
+ * page currently being scanned; and if no identical page is found in the
+ * tree, we insert rmap_item as a new object into the unstable tree.
+ *
+ * This function returns pointer to rmap_item found to be identical
+ * to the currently scanned page, NULL otherwise.
+ *
+ * This function does both searching and inserting, because they share
+ * the same walking algorithm in an rbtree.
+ */
+static
+struct ksm_rmap_item *unstable_tree_search_insert(struct ksm_rmap_item *rmap_item,
+ struct page *page,
+ struct page **tree_pagep)
+{
+ struct rb_node **new;
+ struct rb_root *root;
+ struct rb_node *parent = NULL;
+ int nid;
+
+ nid = get_kpfn_nid(page_to_pfn(page));
+ root = root_unstable_tree + nid;
+ new = &root->rb_node;
+
+ while (*new) {
+ struct ksm_rmap_item *tree_rmap_item;
+ struct page *tree_page;
+ int ret;
+
+ cond_resched();
+ tree_rmap_item = rb_entry(*new, struct ksm_rmap_item, node);
+ tree_page = get_mergeable_page(tree_rmap_item);
+ if (!tree_page)
+ return NULL;
+
+ /*
+ * Don't substitute a ksm page for a forked page.
+ */
+ if (page == tree_page) {
+ put_page(tree_page);
+ return NULL;
+ }
+
+ ret = memcmp_pages(page, tree_page);
+
+ parent = *new;
+ if (ret < 0) {
+ put_page(tree_page);
+ new = &parent->rb_left;
+ } else if (ret > 0) {
+ put_page(tree_page);
+ new = &parent->rb_right;
+ } else if (!ksm_merge_across_nodes &&
+ page_to_nid(tree_page) != nid) {
+ /*
+ * If tree_page has been migrated to another NUMA node,
+ * it will be flushed out and put in the right unstable
+ * tree next time: only merge with it when across_nodes.
+ */
+ put_page(tree_page);
+ return NULL;
+ } else {
+ *tree_pagep = tree_page;
+ return tree_rmap_item;
+ }
+ }
+
+ rmap_item->address |= UNSTABLE_FLAG;
+ rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
+ DO_NUMA(rmap_item->nid = nid);
+ rb_link_node(&rmap_item->node, parent, new);
+ rb_insert_color(&rmap_item->node, root);
+
+ ksm_pages_unshared++;
+ return NULL;
+}
+
+/*
+ * stable_tree_append - add another rmap_item to the linked list of
+ * rmap_items hanging off a given node of the stable tree, all sharing
+ * the same ksm page.
+ */
+static void stable_tree_append(struct ksm_rmap_item *rmap_item,
+ struct ksm_stable_node *stable_node,
+ bool max_page_sharing_bypass)
+{
+ /*
+ * rmap won't find this mapping if we don't insert the
+ * rmap_item in the right stable_node
+ * duplicate. page_migration could break later if rmap breaks,
+ * so we can as well crash here. We really need to check for
+ * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
+ * for other negative values as an underflow if detected here
+ * for the first time (and not when decreasing rmap_hlist_len)
+ * would be sign of memory corruption in the stable_node.
+ */
+ BUG_ON(stable_node->rmap_hlist_len < 0);
+
+ stable_node->rmap_hlist_len++;
+ if (!max_page_sharing_bypass)
+ /* possibly non fatal but unexpected overflow, only warn */
+ WARN_ON_ONCE(stable_node->rmap_hlist_len >
+ ksm_max_page_sharing);
+
+ rmap_item->head = stable_node;
+ rmap_item->address |= STABLE_FLAG;
+ hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
+
+ if (rmap_item->hlist.next)
+ ksm_pages_sharing++;
+ else
+ ksm_pages_shared++;
+
+ rmap_item->mm->ksm_merging_pages++;
+}
+
+/*
+ * cmp_and_merge_page - first see if page can be merged into the stable tree;
+ * if not, compare checksum to previous and if it's the same, see if page can
+ * be inserted into the unstable tree, or merged with a page already there and
+ * both transferred to the stable tree.
+ *
+ * @page: the page that we are searching identical page to.
+ * @rmap_item: the reverse mapping into the virtual address of this page
+ */
+static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_item)
+{
+ struct mm_struct *mm = rmap_item->mm;
+ struct ksm_rmap_item *tree_rmap_item;
+ struct page *tree_page = NULL;
+ struct ksm_stable_node *stable_node;
+ struct page *kpage;
+ unsigned int checksum;
+ int err;
+ bool max_page_sharing_bypass = false;
+
+ stable_node = page_stable_node(page);
+ if (stable_node) {
+ if (stable_node->head != &migrate_nodes &&
+ get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
+ NUMA(stable_node->nid)) {
+ stable_node_dup_del(stable_node);
+ stable_node->head = &migrate_nodes;
+ list_add(&stable_node->list, stable_node->head);
+ }
+ if (stable_node->head != &migrate_nodes &&
+ rmap_item->head == stable_node)
+ return;
+ /*
+ * If it's a KSM fork, allow it to go over the sharing limit
+ * without warnings.
+ */
+ if (!is_page_sharing_candidate(stable_node))
+ max_page_sharing_bypass = true;
+ }
+
+ /* We first start with searching the page inside the stable tree */
+ kpage = stable_tree_search(page);
+ if (kpage == page && rmap_item->head == stable_node) {
+ put_page(kpage);
+ return;
+ }
+
+ remove_rmap_item_from_tree(rmap_item);
+
+ if (kpage) {
+ if (PTR_ERR(kpage) == -EBUSY)
+ return;
+
+ err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
+ if (!err) {
+ /*
+ * The page was successfully merged:
+ * add its rmap_item to the stable tree.
+ */
+ lock_page(kpage);
+ stable_tree_append(rmap_item, page_stable_node(kpage),
+ max_page_sharing_bypass);
+ unlock_page(kpage);
+ }
+ put_page(kpage);
+ return;
+ }
+
+ /*
+ * If the hash value of the page has changed from the last time
+ * we calculated it, this page is changing frequently: therefore we
+ * don't want to insert it in the unstable tree, and we don't want
+ * to waste our time searching for something identical to it there.
+ */
+ checksum = calc_checksum(page);
+ if (rmap_item->oldchecksum != checksum) {
+ rmap_item->oldchecksum = checksum;
+ return;
+ }
+
+ /*
+ * Same checksum as an empty page. We attempt to merge it with the
+ * appropriate zero page if the user enabled this via sysfs.
+ */
+ if (ksm_use_zero_pages && (checksum == zero_checksum)) {
+ struct vm_area_struct *vma;
+
+ mmap_read_lock(mm);
+ vma = find_mergeable_vma(mm, rmap_item->address);
+ if (vma) {
+ err = try_to_merge_one_page(vma, page,
+ ZERO_PAGE(rmap_item->address));
+ } else {
+ /*
+ * If the vma is out of date, we do not need to
+ * continue.
+ */
+ err = 0;
+ }
+ mmap_read_unlock(mm);
+ /*
+ * In case of failure, the page was not really empty, so we
+ * need to continue. Otherwise we're done.
+ */
+ if (!err)
+ return;
+ }
+ tree_rmap_item =
+ unstable_tree_search_insert(rmap_item, page, &tree_page);
+ if (tree_rmap_item) {
+ bool split;
+
+ kpage = try_to_merge_two_pages(rmap_item, page,
+ tree_rmap_item, tree_page);
+ /*
+ * If both pages we tried to merge belong to the same compound
+ * page, then we actually ended up increasing the reference
+ * count of the same compound page twice, and split_huge_page
+ * failed.
+ * Here we set a flag if that happened, and we use it later to
+ * try split_huge_page again. Since we call put_page right
+ * afterwards, the reference count will be correct and
+ * split_huge_page should succeed.
+ */
+ split = PageTransCompound(page)
+ && compound_head(page) == compound_head(tree_page);
+ put_page(tree_page);
+ if (kpage) {
+ /*
+ * The pages were successfully merged: insert new
+ * node in the stable tree and add both rmap_items.
+ */
+ lock_page(kpage);
+ stable_node = stable_tree_insert(kpage);
+ if (stable_node) {
+ stable_tree_append(tree_rmap_item, stable_node,
+ false);
+ stable_tree_append(rmap_item, stable_node,
+ false);
+ }
+ unlock_page(kpage);
+
+ /*
+ * If we fail to insert the page into the stable tree,
+ * we will have 2 virtual addresses that are pointing
+ * to a ksm page left outside the stable tree,
+ * in which case we need to break_cow on both.
+ */
+ if (!stable_node) {
+ break_cow(tree_rmap_item);
+ break_cow(rmap_item);
+ }
+ } else if (split) {
+ /*
+ * We are here if we tried to merge two pages and
+ * failed because they both belonged to the same
+ * compound page. We will split the page now, but no
+ * merging will take place.
+ * We do not want to add the cost of a full lock; if
+ * the page is locked, it is better to skip it and
+ * perhaps try again later.
+ */
+ if (!trylock_page(page))
+ return;
+ split_huge_page(page);
+ unlock_page(page);
+ }
+ }
+}
+
+static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot,
+ struct ksm_rmap_item **rmap_list,
+ unsigned long addr)
+{
+ struct ksm_rmap_item *rmap_item;
+
+ while (*rmap_list) {
+ rmap_item = *rmap_list;
+ if ((rmap_item->address & PAGE_MASK) == addr)
+ return rmap_item;
+ if (rmap_item->address > addr)
+ break;
+ *rmap_list = rmap_item->rmap_list;
+ remove_rmap_item_from_tree(rmap_item);
+ free_rmap_item(rmap_item);
+ }
+
+ rmap_item = alloc_rmap_item();
+ if (rmap_item) {
+ /* It has already been zeroed */
+ rmap_item->mm = mm_slot->slot.mm;
+ rmap_item->mm->ksm_rmap_items++;
+ rmap_item->address = addr;
+ rmap_item->rmap_list = *rmap_list;
+ *rmap_list = rmap_item;
+ }
+ return rmap_item;
+}
+
+static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
+{
+ struct mm_struct *mm;
+ struct ksm_mm_slot *mm_slot;
+ struct mm_slot *slot;
+ struct vm_area_struct *vma;
+ struct ksm_rmap_item *rmap_item;
+ struct vma_iterator vmi;
+ int nid;
+
+ if (list_empty(&ksm_mm_head.slot.mm_node))
+ return NULL;
+
+ mm_slot = ksm_scan.mm_slot;
+ if (mm_slot == &ksm_mm_head) {
+ /*
+ * A number of pages can hang around indefinitely on per-cpu
+ * pagevecs, raised page count preventing write_protect_page
+ * from merging them. Though it doesn't really matter much,
+ * it is puzzling to see some stuck in pages_volatile until
+ * other activity jostles them out, and they also prevented
+ * LTP's KSM test from succeeding deterministically; so drain
+ * them here (here rather than on entry to ksm_do_scan(),
+ * so we don't IPI too often when pages_to_scan is set low).
+ */
+ lru_add_drain_all();
+
+ /*
+ * Whereas stale stable_nodes on the stable_tree itself
+ * get pruned in the regular course of stable_tree_search(),
+ * those moved out to the migrate_nodes list can accumulate:
+ * so prune them once before each full scan.
+ */
+ if (!ksm_merge_across_nodes) {
+ struct ksm_stable_node *stable_node, *next;
+ struct page *page;
+
+ list_for_each_entry_safe(stable_node, next,
+ &migrate_nodes, list) {
+ page = get_ksm_page(stable_node,
+ GET_KSM_PAGE_NOLOCK);
+ if (page)
+ put_page(page);
+ cond_resched();
+ }
+ }
+
+ for (nid = 0; nid < ksm_nr_node_ids; nid++)
+ root_unstable_tree[nid] = RB_ROOT;
+
+ spin_lock(&ksm_mmlist_lock);
+ slot = list_entry(mm_slot->slot.mm_node.next,
+ struct mm_slot, mm_node);
+ mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+ ksm_scan.mm_slot = mm_slot;
+ spin_unlock(&ksm_mmlist_lock);
+ /*
+ * Although we tested list_empty() above, a racing __ksm_exit
+ * of the last mm on the list may have removed it since then.
+ */
+ if (mm_slot == &ksm_mm_head)
+ return NULL;
+next_mm:
+ ksm_scan.address = 0;
+ ksm_scan.rmap_list = &mm_slot->rmap_list;
+ }
+
+ slot = &mm_slot->slot;
+ mm = slot->mm;
+ vma_iter_init(&vmi, mm, ksm_scan.address);
+
+ mmap_read_lock(mm);
+ if (ksm_test_exit(mm))
+ goto no_vmas;
+
+ for_each_vma(vmi, vma) {
+ if (!(vma->vm_flags & VM_MERGEABLE))
+ continue;
+ if (ksm_scan.address < vma->vm_start)
+ ksm_scan.address = vma->vm_start;
+ if (!vma->anon_vma)
+ ksm_scan.address = vma->vm_end;
+
+ while (ksm_scan.address < vma->vm_end) {
+ if (ksm_test_exit(mm))
+ break;
+ *page = follow_page(vma, ksm_scan.address, FOLL_GET);
+ if (IS_ERR_OR_NULL(*page)) {
+ ksm_scan.address += PAGE_SIZE;
+ cond_resched();
+ continue;
+ }
+ if (is_zone_device_page(*page))
+ goto next_page;
+ if (PageAnon(*page)) {
+ flush_anon_page(vma, *page, ksm_scan.address);
+ flush_dcache_page(*page);
+ rmap_item = get_next_rmap_item(mm_slot,
+ ksm_scan.rmap_list, ksm_scan.address);
+ if (rmap_item) {
+ ksm_scan.rmap_list =
+ &rmap_item->rmap_list;
+ ksm_scan.address += PAGE_SIZE;
+ } else
+ put_page(*page);
+ mmap_read_unlock(mm);
+ return rmap_item;
+ }
+next_page:
+ put_page(*page);
+ ksm_scan.address += PAGE_SIZE;
+ cond_resched();
+ }
+ }
+
+ if (ksm_test_exit(mm)) {
+no_vmas:
+ ksm_scan.address = 0;
+ ksm_scan.rmap_list = &mm_slot->rmap_list;
+ }
+ /*
+ * Nuke all the rmap_items that are above this current rmap:
+ * because there were no VM_MERGEABLE vmas with such addresses.
+ */
+ remove_trailing_rmap_items(ksm_scan.rmap_list);
+
+ spin_lock(&ksm_mmlist_lock);
+ slot = list_entry(mm_slot->slot.mm_node.next,
+ struct mm_slot, mm_node);
+ ksm_scan.mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+ if (ksm_scan.address == 0) {
+ /*
+ * We've completed a full scan of all vmas, holding mmap_lock
+ * throughout, and found no VM_MERGEABLE: so do the same as
+ * __ksm_exit does to remove this mm from all our lists now.
+ * This applies either when cleaning up after __ksm_exit
+ * (but beware: we can reach here even before __ksm_exit),
+ * or when all VM_MERGEABLE areas have been unmapped (and
+ * mmap_lock then protects against race with MADV_MERGEABLE).
+ */
+ hash_del(&mm_slot->slot.hash);
+ list_del(&mm_slot->slot.mm_node);
+ spin_unlock(&ksm_mmlist_lock);
+
+ mm_slot_free(mm_slot_cache, mm_slot);
+ clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+ mmap_read_unlock(mm);
+ mmdrop(mm);
+ } else {
+ mmap_read_unlock(mm);
+ /*
+ * mmap_read_unlock(mm) first because after
+ * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
+ * already have been freed under us by __ksm_exit()
+ * because the "mm_slot" is still hashed and
+ * ksm_scan.mm_slot doesn't point to it anymore.
+ */
+ spin_unlock(&ksm_mmlist_lock);
+ }
+
+ /* Repeat until we've completed scanning the whole list */
+ mm_slot = ksm_scan.mm_slot;
+ if (mm_slot != &ksm_mm_head)
+ goto next_mm;
+
+ ksm_scan.seqnr++;
+ return NULL;
+}
+
+/**
+ * ksm_do_scan - the ksm scanner main worker function.
+ * @scan_npages: number of pages we want to scan before we return.
+ */
+static void ksm_do_scan(unsigned int scan_npages)
+{
+ struct ksm_rmap_item *rmap_item;
+ struct page *page;
+
+ while (scan_npages-- && likely(!freezing(current))) {
+ cond_resched();
+ rmap_item = scan_get_next_rmap_item(&page);
+ if (!rmap_item)
+ return;
+ cmp_and_merge_page(page, rmap_item);
+ put_page(page);
+ }
+}
+
+static int ksmd_should_run(void)
+{
+ return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.slot.mm_node);
+}
+
+static int ksm_scan_thread(void *nothing)
+{
+ unsigned int sleep_ms;
+
+ set_freezable();
+ set_user_nice(current, 5);
+
+ while (!kthread_should_stop()) {
+ mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
+ if (ksmd_should_run())
+ ksm_do_scan(ksm_thread_pages_to_scan);
+ mutex_unlock(&ksm_thread_mutex);
+
+ try_to_freeze();
+
+ if (ksmd_should_run()) {
+ sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
+ wait_event_interruptible_timeout(ksm_iter_wait,
+ sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
+ msecs_to_jiffies(sleep_ms));
+ } else {
+ wait_event_freezable(ksm_thread_wait,
+ ksmd_should_run() || kthread_should_stop());
+ }
+ }
+ return 0;
+}
+
+int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
+ unsigned long end, int advice, unsigned long *vm_flags)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ int err;
+
+ switch (advice) {
+ case MADV_MERGEABLE:
+ /*
+ * Be somewhat over-protective for now!
+ */
+ if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
+ VM_PFNMAP | VM_IO | VM_DONTEXPAND |
+ VM_HUGETLB | VM_MIXEDMAP))
+ return 0; /* just ignore the advice */
+
+ if (vma_is_dax(vma))
+ return 0;
+
+#ifdef VM_SAO
+ if (*vm_flags & VM_SAO)
+ return 0;
+#endif
+#ifdef VM_SPARC_ADI
+ if (*vm_flags & VM_SPARC_ADI)
+ return 0;
+#endif
+
+ if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
+ err = __ksm_enter(mm);
+ if (err)
+ return err;
+ }
+
+ *vm_flags |= VM_MERGEABLE;
+ break;
+
+ case MADV_UNMERGEABLE:
+ if (!(*vm_flags & VM_MERGEABLE))
+ return 0; /* just ignore the advice */
+
+ if (vma->anon_vma) {
+ err = unmerge_ksm_pages(vma, start, end);
+ if (err)
+ return err;
+ }
+
+ *vm_flags &= ~VM_MERGEABLE;
+ break;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(ksm_madvise);
+
+int __ksm_enter(struct mm_struct *mm)
+{
+ struct ksm_mm_slot *mm_slot;
+ struct mm_slot *slot;
+ int needs_wakeup;
+
+ mm_slot = mm_slot_alloc(mm_slot_cache);
+ if (!mm_slot)
+ return -ENOMEM;
+
+ slot = &mm_slot->slot;
+
+ /* Check ksm_run too? Would need tighter locking */
+ needs_wakeup = list_empty(&ksm_mm_head.slot.mm_node);
+
+ spin_lock(&ksm_mmlist_lock);
+ mm_slot_insert(mm_slots_hash, mm, slot);
+ /*
+ * When KSM_RUN_MERGE (or KSM_RUN_STOP),
+ * insert just behind the scanning cursor, to let the area settle
+ * down a little; when fork is followed by immediate exec, we don't
+ * want ksmd to waste time setting up and tearing down an rmap_list.
+ *
+ * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
+ * scanning cursor, otherwise KSM pages in newly forked mms will be
+ * missed: then we might as well insert at the end of the list.
+ */
+ if (ksm_run & KSM_RUN_UNMERGE)
+ list_add_tail(&slot->mm_node, &ksm_mm_head.slot.mm_node);
+ else
+ list_add_tail(&slot->mm_node, &ksm_scan.mm_slot->slot.mm_node);
+ spin_unlock(&ksm_mmlist_lock);
+
+ set_bit(MMF_VM_MERGEABLE, &mm->flags);
+ mmgrab(mm);
+
+ if (needs_wakeup)
+ wake_up_interruptible(&ksm_thread_wait);
+
+ return 0;
+}
+
+void __ksm_exit(struct mm_struct *mm)
+{
+ struct ksm_mm_slot *mm_slot;
+ struct mm_slot *slot;
+ int easy_to_free = 0;
+
+ /*
+ * This process is exiting: if it's straightforward (as is the
+ * case when ksmd was never running), free mm_slot immediately.
+ * But if it's at the cursor or has rmap_items linked to it, use
+ * mmap_lock to synchronize with any break_cows before pagetables
+ * are freed, and leave the mm_slot on the list for ksmd to free.
+ * Beware: ksm may already have noticed it exiting and freed the slot.
+ */
+
+ spin_lock(&ksm_mmlist_lock);
+ slot = mm_slot_lookup(mm_slots_hash, mm);
+ mm_slot = mm_slot_entry(slot, struct ksm_mm_slot, slot);
+ if (mm_slot && ksm_scan.mm_slot != mm_slot) {
+ if (!mm_slot->rmap_list) {
+ hash_del(&slot->hash);
+ list_del(&slot->mm_node);
+ easy_to_free = 1;
+ } else {
+ list_move(&slot->mm_node,
+ &ksm_scan.mm_slot->slot.mm_node);
+ }
+ }
+ spin_unlock(&ksm_mmlist_lock);
+
+ if (easy_to_free) {
+ mm_slot_free(mm_slot_cache, mm_slot);
+ clear_bit(MMF_VM_MERGEABLE, &mm->flags);
+ mmdrop(mm);
+ } else if (mm_slot) {
+ mmap_write_lock(mm);
+ mmap_write_unlock(mm);
+ }
+}
+
+struct page *ksm_might_need_to_copy(struct page *page,
+ struct vm_area_struct *vma, unsigned long address)
+{
+ struct folio *folio = page_folio(page);
+ struct anon_vma *anon_vma = folio_anon_vma(folio);
+ struct page *new_page;
+
+ if (PageKsm(page)) {
+ if (page_stable_node(page) &&
+ !(ksm_run & KSM_RUN_UNMERGE))
+ return page; /* no need to copy it */
+ } else if (!anon_vma) {
+ return page; /* no need to copy it */
+ } else if (page->index == linear_page_index(vma, address) &&
+ anon_vma->root == vma->anon_vma->root) {
+ return page; /* still no need to copy it */
+ }
+ if (!PageUptodate(page))
+ return page; /* let do_swap_page report the error */
+
+ new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
+ if (new_page &&
+ mem_cgroup_charge(page_folio(new_page), vma->vm_mm, GFP_KERNEL)) {
+ put_page(new_page);
+ new_page = NULL;
+ }
+ if (new_page) {
+ copy_user_highpage(new_page, page, address, vma);
+
+ SetPageDirty(new_page);
+ __SetPageUptodate(new_page);
+ __SetPageLocked(new_page);
+#ifdef CONFIG_SWAP
+ count_vm_event(KSM_SWPIN_COPY);
+#endif
+ }
+
+ return new_page;
+}
+
+void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc)
+{
+ struct ksm_stable_node *stable_node;
+ struct ksm_rmap_item *rmap_item;
+ int search_new_forks = 0;
+
+ VM_BUG_ON_FOLIO(!folio_test_ksm(folio), folio);
+
+ /*
+ * Rely on the page lock to protect against concurrent modifications
+ * to that page's node of the stable tree.
+ */
+ VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+ stable_node = folio_stable_node(folio);
+ if (!stable_node)
+ return;
+again:
+ hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
+ struct anon_vma *anon_vma = rmap_item->anon_vma;
+ struct anon_vma_chain *vmac;
+ struct vm_area_struct *vma;
+
+ cond_resched();
+ if (!anon_vma_trylock_read(anon_vma)) {
+ if (rwc->try_lock) {
+ rwc->contended = true;
+ return;
+ }
+ anon_vma_lock_read(anon_vma);
+ }
+ anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
+ 0, ULONG_MAX) {
+ unsigned long addr;
+
+ cond_resched();
+ vma = vmac->vma;
+
+ /* Ignore the stable/unstable/sqnr flags */
+ addr = rmap_item->address & PAGE_MASK;
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ continue;
+ /*
+ * Initially we examine only the vma which covers this
+ * rmap_item; but later, if there is still work to do,
+ * we examine covering vmas in other mms: in case they
+ * were forked from the original since ksmd passed.
+ */
+ if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
+ continue;
+
+ if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
+ continue;
+
+ if (!rwc->rmap_one(folio, vma, addr, rwc->arg)) {
+ anon_vma_unlock_read(anon_vma);
+ return;
+ }
+ if (rwc->done && rwc->done(folio)) {
+ anon_vma_unlock_read(anon_vma);
+ return;
+ }
+ }
+ anon_vma_unlock_read(anon_vma);
+ }
+ if (!search_new_forks++)
+ goto again;
+}
+
+#ifdef CONFIG_MIGRATION
+void folio_migrate_ksm(struct folio *newfolio, struct folio *folio)
+{
+ struct ksm_stable_node *stable_node;
+
+ VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+ VM_BUG_ON_FOLIO(!folio_test_locked(newfolio), newfolio);
+ VM_BUG_ON_FOLIO(newfolio->mapping != folio->mapping, newfolio);
+
+ stable_node = folio_stable_node(folio);
+ if (stable_node) {
+ VM_BUG_ON_FOLIO(stable_node->kpfn != folio_pfn(folio), folio);
+ stable_node->kpfn = folio_pfn(newfolio);
+ /*
+ * newfolio->mapping was set in advance; now we need smp_wmb()
+ * to make sure that the new stable_node->kpfn is visible
+ * to get_ksm_page() before it can see that folio->mapping
+ * has gone stale (or that folio_test_swapcache has been cleared).
+ */
+ smp_wmb();
+ set_page_stable_node(&folio->page, NULL);
+ }
+}
+#endif /* CONFIG_MIGRATION */
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static void wait_while_offlining(void)
+{
+ while (ksm_run & KSM_RUN_OFFLINE) {
+ mutex_unlock(&ksm_thread_mutex);
+ wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
+ TASK_UNINTERRUPTIBLE);
+ mutex_lock(&ksm_thread_mutex);
+ }
+}
+
+static bool stable_node_dup_remove_range(struct ksm_stable_node *stable_node,
+ unsigned long start_pfn,
+ unsigned long end_pfn)
+{
+ if (stable_node->kpfn >= start_pfn &&
+ stable_node->kpfn < end_pfn) {
+ /*
+ * Don't get_ksm_page, page has already gone:
+ * which is why we keep kpfn instead of page*
+ */
+ remove_node_from_stable_tree(stable_node);
+ return true;
+ }
+ return false;
+}
+
+static bool stable_node_chain_remove_range(struct ksm_stable_node *stable_node,
+ unsigned long start_pfn,
+ unsigned long end_pfn,
+ struct rb_root *root)
+{
+ struct ksm_stable_node *dup;
+ struct hlist_node *hlist_safe;
+
+ if (!is_stable_node_chain(stable_node)) {
+ VM_BUG_ON(is_stable_node_dup(stable_node));
+ return stable_node_dup_remove_range(stable_node, start_pfn,
+ end_pfn);
+ }
+
+ hlist_for_each_entry_safe(dup, hlist_safe,
+ &stable_node->hlist, hlist_dup) {
+ VM_BUG_ON(!is_stable_node_dup(dup));
+ stable_node_dup_remove_range(dup, start_pfn, end_pfn);
+ }
+ if (hlist_empty(&stable_node->hlist)) {
+ free_stable_node_chain(stable_node, root);
+ return true; /* notify caller that tree was rebalanced */
+ } else
+ return false;
+}
+
+static void ksm_check_stable_tree(unsigned long start_pfn,
+ unsigned long end_pfn)
+{
+ struct ksm_stable_node *stable_node, *next;
+ struct rb_node *node;
+ int nid;
+
+ for (nid = 0; nid < ksm_nr_node_ids; nid++) {
+ node = rb_first(root_stable_tree + nid);
+ while (node) {
+ stable_node = rb_entry(node, struct ksm_stable_node, node);
+ if (stable_node_chain_remove_range(stable_node,
+ start_pfn, end_pfn,
+ root_stable_tree +
+ nid))
+ node = rb_first(root_stable_tree + nid);
+ else
+ node = rb_next(node);
+ cond_resched();
+ }
+ }
+ list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
+ if (stable_node->kpfn >= start_pfn &&
+ stable_node->kpfn < end_pfn)
+ remove_node_from_stable_tree(stable_node);
+ cond_resched();
+ }
+}
+
+static int ksm_memory_callback(struct notifier_block *self,
+ unsigned long action, void *arg)
+{
+ struct memory_notify *mn = arg;
+
+ switch (action) {
+ case MEM_GOING_OFFLINE:
+ /*
+ * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
+ * and remove_all_stable_nodes() while memory is going offline:
+ * it is unsafe for them to touch the stable tree at this time.
+ * But unmerge_ksm_pages(), rmap lookups and other entry points
+ * which do not need the ksm_thread_mutex are all safe.
+ */
+ mutex_lock(&ksm_thread_mutex);
+ ksm_run |= KSM_RUN_OFFLINE;
+ mutex_unlock(&ksm_thread_mutex);
+ break;
+
+ case MEM_OFFLINE:
+ /*
+ * Most of the work is done by page migration; but there might
+ * be a few stable_nodes left over, still pointing to struct
+ * pages which have been offlined: prune those from the tree,
+ * otherwise get_ksm_page() might later try to access a
+ * non-existent struct page.
+ */
+ ksm_check_stable_tree(mn->start_pfn,
+ mn->start_pfn + mn->nr_pages);
+ fallthrough;
+ case MEM_CANCEL_OFFLINE:
+ mutex_lock(&ksm_thread_mutex);
+ ksm_run &= ~KSM_RUN_OFFLINE;
+ mutex_unlock(&ksm_thread_mutex);
+
+ smp_mb(); /* wake_up_bit advises this */
+ wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
+ break;
+ }
+ return NOTIFY_OK;
+}
+#else
+static void wait_while_offlining(void)
+{
+}
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+
+#ifdef CONFIG_SYSFS
+/*
+ * This all compiles without CONFIG_SYSFS, but is a waste of space.
+ */
+
+#define KSM_ATTR_RO(_name) \
+ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+#define KSM_ATTR(_name) \
+ static struct kobj_attribute _name##_attr = __ATTR_RW(_name)
+
+static ssize_t sleep_millisecs_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
+}
+
+static ssize_t sleep_millisecs_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int msecs;
+ int err;
+
+ err = kstrtouint(buf, 10, &msecs);
+ if (err)
+ return -EINVAL;
+
+ ksm_thread_sleep_millisecs = msecs;
+ wake_up_interruptible(&ksm_iter_wait);
+
+ return count;
+}
+KSM_ATTR(sleep_millisecs);
+
+static ssize_t pages_to_scan_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
+}
+
+static ssize_t pages_to_scan_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int nr_pages;
+ int err;
+
+ err = kstrtouint(buf, 10, &nr_pages);
+ if (err)
+ return -EINVAL;
+
+ ksm_thread_pages_to_scan = nr_pages;
+
+ return count;
+}
+KSM_ATTR(pages_to_scan);
+
+static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_run);
+}
+
+static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int flags;
+ int err;
+
+ err = kstrtouint(buf, 10, &flags);
+ if (err)
+ return -EINVAL;
+ if (flags > KSM_RUN_UNMERGE)
+ return -EINVAL;
+
+ /*
+ * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
+ * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
+ * breaking COW to free the pages_shared (but leaves mm_slots
+ * on the list for when ksmd may be set running again).
+ */
+
+ mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
+ if (ksm_run != flags) {
+ ksm_run = flags;
+ if (flags & KSM_RUN_UNMERGE) {
+ set_current_oom_origin();
+ err = unmerge_and_remove_all_rmap_items();
+ clear_current_oom_origin();
+ if (err) {
+ ksm_run = KSM_RUN_STOP;
+ count = err;
+ }
+ }
+ }
+ mutex_unlock(&ksm_thread_mutex);
+
+ if (flags & KSM_RUN_MERGE)
+ wake_up_interruptible(&ksm_thread_wait);
+
+ return count;
+}
+KSM_ATTR(run);
+
+#ifdef CONFIG_NUMA
+static ssize_t merge_across_nodes_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
+}
+
+static ssize_t merge_across_nodes_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ unsigned long knob;
+
+ err = kstrtoul(buf, 10, &knob);
+ if (err)
+ return err;
+ if (knob > 1)
+ return -EINVAL;
+
+ mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
+ if (ksm_merge_across_nodes != knob) {
+ if (ksm_pages_shared || remove_all_stable_nodes())
+ err = -EBUSY;
+ else if (root_stable_tree == one_stable_tree) {
+ struct rb_root *buf;
+ /*
+ * This is the first time that we switch away from the
+ * default of merging across nodes: must now allocate
+ * a buffer to hold as many roots as may be needed.
+ * Allocate stable and unstable together:
+ * MAXSMP NODES_SHIFT 10 will use 16kB.
+ */
+ buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
+ GFP_KERNEL);
+ /* Let us assume that RB_ROOT is NULL is zero */
+ if (!buf)
+ err = -ENOMEM;
+ else {
+ root_stable_tree = buf;
+ root_unstable_tree = buf + nr_node_ids;
+ /* Stable tree is empty but not the unstable */
+ root_unstable_tree[0] = one_unstable_tree[0];
+ }
+ }
+ if (!err) {
+ ksm_merge_across_nodes = knob;
+ ksm_nr_node_ids = knob ? 1 : nr_node_ids;
+ }
+ }
+ mutex_unlock(&ksm_thread_mutex);
+
+ return err ? err : count;
+}
+KSM_ATTR(merge_across_nodes);
+#endif
+
+static ssize_t use_zero_pages_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
+}
+static ssize_t use_zero_pages_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ bool value;
+
+ err = kstrtobool(buf, &value);
+ if (err)
+ return -EINVAL;
+
+ ksm_use_zero_pages = value;
+
+ return count;
+}
+KSM_ATTR(use_zero_pages);
+
+static ssize_t max_page_sharing_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
+}
+
+static ssize_t max_page_sharing_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ int err;
+ int knob;
+
+ err = kstrtoint(buf, 10, &knob);
+ if (err)
+ return err;
+ /*
+ * When a KSM page is created it is shared by 2 mappings. This
+ * being a signed comparison, it implicitly verifies it's not
+ * negative.
+ */
+ if (knob < 2)
+ return -EINVAL;
+
+ if (READ_ONCE(ksm_max_page_sharing) == knob)
+ return count;
+
+ mutex_lock(&ksm_thread_mutex);
+ wait_while_offlining();
+ if (ksm_max_page_sharing != knob) {
+ if (ksm_pages_shared || remove_all_stable_nodes())
+ err = -EBUSY;
+ else
+ ksm_max_page_sharing = knob;
+ }
+ mutex_unlock(&ksm_thread_mutex);
+
+ return err ? err : count;
+}
+KSM_ATTR(max_page_sharing);
+
+static ssize_t pages_shared_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
+}
+KSM_ATTR_RO(pages_shared);
+
+static ssize_t pages_sharing_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
+}
+KSM_ATTR_RO(pages_sharing);
+
+static ssize_t pages_unshared_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
+}
+KSM_ATTR_RO(pages_unshared);
+
+static ssize_t pages_volatile_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ long ksm_pages_volatile;
+
+ ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
+ - ksm_pages_sharing - ksm_pages_unshared;
+ /*
+ * It was not worth any locking to calculate that statistic,
+ * but it might therefore sometimes be negative: conceal that.
+ */
+ if (ksm_pages_volatile < 0)
+ ksm_pages_volatile = 0;
+ return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
+}
+KSM_ATTR_RO(pages_volatile);
+
+static ssize_t stable_node_dups_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
+}
+KSM_ATTR_RO(stable_node_dups);
+
+static ssize_t stable_node_chains_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
+}
+KSM_ATTR_RO(stable_node_chains);
+
+static ssize_t
+stable_node_chains_prune_millisecs_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
+}
+
+static ssize_t
+stable_node_chains_prune_millisecs_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ unsigned int msecs;
+ int err;
+
+ err = kstrtouint(buf, 10, &msecs);
+ if (err)
+ return -EINVAL;
+
+ ksm_stable_node_chains_prune_millisecs = msecs;
+
+ return count;
+}
+KSM_ATTR(stable_node_chains_prune_millisecs);
+
+static ssize_t full_scans_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
+}
+KSM_ATTR_RO(full_scans);
+
+static struct attribute *ksm_attrs[] = {
+ &sleep_millisecs_attr.attr,
+ &pages_to_scan_attr.attr,
+ &run_attr.attr,
+ &pages_shared_attr.attr,
+ &pages_sharing_attr.attr,
+ &pages_unshared_attr.attr,
+ &pages_volatile_attr.attr,
+ &full_scans_attr.attr,
+#ifdef CONFIG_NUMA
+ &merge_across_nodes_attr.attr,
+#endif
+ &max_page_sharing_attr.attr,
+ &stable_node_chains_attr.attr,
+ &stable_node_dups_attr.attr,
+ &stable_node_chains_prune_millisecs_attr.attr,
+ &use_zero_pages_attr.attr,
+ NULL,
+};
+
+static const struct attribute_group ksm_attr_group = {
+ .attrs = ksm_attrs,
+ .name = "ksm",
+};
+#endif /* CONFIG_SYSFS */
+
+static int __init ksm_init(void)
+{
+ struct task_struct *ksm_thread;
+ int err;
+
+ /* The correct value depends on page size and endianness */
+ zero_checksum = calc_checksum(ZERO_PAGE(0));
+ /* Default to false for backwards compatibility */
+ ksm_use_zero_pages = false;
+
+ err = ksm_slab_init();
+ if (err)
+ goto out;
+
+ ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
+ if (IS_ERR(ksm_thread)) {
+ pr_err("ksm: creating kthread failed\n");
+ err = PTR_ERR(ksm_thread);
+ goto out_free;
+ }
+
+#ifdef CONFIG_SYSFS
+ err = sysfs_create_group(mm_kobj, &ksm_attr_group);
+ if (err) {
+ pr_err("ksm: register sysfs failed\n");
+ kthread_stop(ksm_thread);
+ goto out_free;
+ }
+#else
+ ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
+
+#endif /* CONFIG_SYSFS */
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+ /* There is no significance to this priority 100 */
+ hotplug_memory_notifier(ksm_memory_callback, 100);
+#endif
+ return 0;
+
+out_free:
+ ksm_slab_free();
+out:
+ return err;
+}
+subsys_initcall(ksm_init);